1. Field of the Invention
The present invention relates to a Time Division Multiple Access (TDMA) communications apparatus for carrying out communication using TDMA technology in which a frame is divided into a plurality of time slots, a slot being treated as a unit of data transmission.
2. Description of the Related Art
In a TDMA communication system, each successive frame is divided into a plurality of time slots based on a common time reference (time base) obtained from the global positioning system (GPS), for example, thereby establishing accurate slot synchronization among a plurality of participating stations (e.g. mobile units such as ships). The participating stations carry out TDMA communication while reserving (allocating) slots for their own transmission of information and messages. In this kind of communication system, such as the Universal Automatic Identification System (UAIS) of which carriage has been required on particular classes of ships since 2002, it is essential for every participating station to communicate data in accordance with defined protocols. To enable proper slot allocation for transmission of information and messages by multiple users in the UAIS, international and national standards set out detailed technical operational rules and specifications including Self-Organized Time Division Multiple Access (SOTDMA).
One problem in the TDMA communication system is that if any user obviously violates the relevant standards or rules, such as UAIS access protocols, or acts against the spirit underlying the standards and rules, a serious difficulty occurs in the operation of the UAIS, resulting in an inability to ensure efficient and safe navigation of ships.